Means for treating thixotropic materials



June 19, 1951 H. M. PREUSSER 2,557,841

MEANS FOR TREATING THIXOTROPIC MATERIALS Filed May 16, 1949 l'mnentorPatented June 19, 1951 UNITED STATE s PATENT OFFICE MEANS FOR TREATINGMATERIALS 'rmxo'raorrc Henry M. Preusser, Seattle, Wash, assignor-toAmerican-Marietta Company, Adhesive, Resin,

and Chemical Division,

notation of Illinois Seattle, Wash., a cor- Application May 16, 1949,Serial No. 93,606 3 Claims. (01. 259 -1) tated as by stirring orshaking, and of resolidi- 'fying or coagulating when again allowed tocome to rest. Hence, a thixotropic material is any material that tendsto gel but can reversibly be made fluid under mechanical action. I havefound that a shearing action is suitable for returning certain gelledthixotropic materials toa state of mobility of fluidity.

In connection with the present invention, I particularlyhave in mindsoya bean meals of the type useful in the adhesives industry forforminga glue line between pieces of woody or similar material.- Soya mealadhesives are commonly used in gluing up veneers to form plywood and,there, probably find their greatest use. Until about 1945 soya beanmeals were produced by what is known as expelling presses, which asqueezed the oil of the ground beans and largely characteristicsmanifested themselves. in gluemixes, for. example, by undesirableincreases of viscosity in a batch of glue. For the purpose of decreasingviscosity it has been the practice of the workers in the art to employchemical materials such as addedamounts of caustic. Such a tended, and,more particularly, to reduce viscosity in proteinous glue mixes withoutharm to the adhesive characteristics of the glue.

At about the time-of the cessation of recent hostilities, solventextraction became widespread, due to the availability of petroleumcomponents and, particularly, hexane which washes the oil out of themeal to a much higher degree than \previously was possible. The'solventextraction process, however, is accompanied by its own peculiarproblems, one of them being the removal of the hexane that is entrappedin-the meal following oil extraction. Not much is known about thevarious processors methods of remov ing the residual hexane, but it isknown that such follow two lines of attack. One is-to heat the meal toabove the boiling point of the hexane to cause the latter to volatizeand go ofi in a practice is set forth in the Laucks et a1. Patent No.1,903,172, particularly in claim 10, wherein these patentees prescribedthe step of adding an additional amount of caustic material for thepurpose of reducing viscosity. The end result 4 of lower viscosity wasthere obtained but to the detriment of the glue mix because of thedenaturing of the protein in the mix which caused a loss of desirableadhesive properties. It is obvious that such practices are undesirableand gaseous form. This causes denaturing of the protein. The otherapparently involves the use of less heat and includes a bath of hexanevapor which seems to extract and absorb the entrapped hexane from themeal. Where the meal is heated substantially it has less desirablecharacteristics from an adhesive standpoint including being thixotropic.Where the meal is subjected to a minimum of heat, it has superioradhesive properties but is highly soluble, tends to lump in aqueousmixtures, foams unreasonably, and has a. low viscosity characteristiccoupled with excessive thickening when the mix is allowed to stand. Inother words, such meal is highly thixotropic. This latter meal isdescribed in the trade as a green meal," for the reason that it has agreen odor reminiscent of green alfalfa.

Adhesives formed of this green meal have been practically impossible touse in, for example, theplywood industry for the reason that when auseful sized batch of adhesive is compounded for use in' the gluespreaders, it would gel so fast and so firmly before it could normallybe used, that it would not readily flow by gravity nor could it bepumped to the point of use. of course, small batches used immediatelyafter compounding would flow and spread but that would necessitateconstant glue batch preparation which is not practical. However, it iseasily to be established that adhesive formed of green meal, .if it canbe handled practically, produces a worthwhile product, because of itssuperior adhesive and bonding qualities in a plywood panel. Such a mealis valuable because of the low degree of protein heat-denaturation. But

such a meal requires, ior practical use as an adhesive, control offoaming, avoidance of lumping and elimination of excess viscosity causedby thixctropy, but without water or caustic treatments to maintain thiscontrol.

Among the important objects of this invention have been the provision ofa method of treating thixotropic materials to maintain them in a mobileor fluid condition desirable for their use;

of a method for treating such materials, when formed of green or othersoya meal, tomake it possible to use such meal in the glue spreadingoperation of a woodworking plant, and, particularly, in plywood mills;of apparatus for treating thixctropic adhesive materials of green mealderivation to impart mobility and fluidity to the same to make themuseful in presently employed conveying and spreading equipment; of amethod and means for imparting a shearing action to such materials in amanner as to produce fluidity while preventing or precluding theentrainment of air and the tendency of the material to form in anundesirable manner; of aprocess and apparatus employing fluid and mobileadhesives exemplifying situations and the methods and the operation wasconducted in the open, there apparatus by which m invention ispracticed.

But flrst, briefly, I have discovered that adhesives formed of greenmeal are thixotropic and can be returned to a mobile state after gellingby subjecting them to a shearing action of a mechanical nature. I havefurther discovered from my work with the material that such shearing asis performed on the adhesives must be conducted under submergedconditions in a manner that air cannot get into the adhesive as it isbeing mechanically worked; otherwise so much air is entrained in thematerial that it becomes excessively foamy and unuseful for glue fllmsin the plywood field. I have further discovered that once a. gelledmaterial has been again made mobile and is then returned to a mass ofgelled material in a dispersed manner, it will tend to make fluid acertain portion of the gelled material. In this latter respect I amreferring to recirculating the mobile and fluid adhesive material backto the batch from which it was drawn so as to maintain a fairly highfluidity within the batch container and so that a constant gravityactuated or pressurized stream flowing tothe glue spreaders can be had.

I first observed the phenomena of thixotropy in green soya mealadhesives in a mill where trouble was being encountered with glue thatgelled too rapidly and would not maintain a feeding stream from the gluepot to the spreader. When the viscosity of this glue was reduced in thepot by the addition of caustic material, or water, the stream to thespreader could be maintained but by the time that the material had pwsedbetween the doctor and the applicator rolls of the spreader, it hadbecome so thin that it was not practically useful for forming a glueline on veneer. When a portion of gelled glue was no demand for glue.

was an entrainment of air that resulted in some undesirable foaming ofthe material.

I have carried forward the thought of employing a mechanical shearingaction on the gelled or gelling material with considerable success underthe actual working conditions found in plywood mills. Highly acceptableresults were obtained by withdrawing portions of gelled material fromthe contents of the glue pot and subjecting such withdrawn material to amechani cal shearing action under submerged conditions to preclude theentrainment of air and in a manner that all the material was caused tobe sheared. While practical results were had by performing the shearingaction with a wire whisk so operated that no vortices were created andonly a minimum of surface break occurred, the most practical method ofmaking fluid the gelled material was to withdraw portions 01' gelledglue from the bottom of the glue pot and introduce it immediately intothe chamber of a gear pump where it rapidly become fluid to a degreethat permitted its conduction in pipes reasonable distances to a gluespreader. It was found that since glue application in the plywood millwas not constant, there were intervals when there During thoseintervals, which are fairly regular and usually protracted, the outflowfrom the pump was returned to the glue pot in a closed circuitoperation. It was found not satisfactory to let the return flow plop orsplash into the pot for the reason that it tended to foam the materialvery undesirably. If the returning stream had substantial pressure andwas fairly solid, it tended to cut through the gelling glue in the potand pass directly to the outlet from the pot without material effect onthe gelled glue in the pot. To overcome this defect, I then arrangedthat the glue be discharged into the pot upon a conical distributor headwhich gradually decreased and decelerated the flow and spread it over awide area of the gelled glue. It was thereupon observed that the morefluid the returning glue material was, the more it tended to make fluidthe gelled material of the pot and to thus facilitate its beingmaintained in fluidity. As a result of this work, I have determined thatthe process best adapted to the practical conditions of handling highlythixotropic glue materials in plywood mills, is to, between theintermittent intervals of withdrawal of glue from the system to supplythe spreaders, withdraw portions of the adhesive composition and tosubject it to a submerged mechanical shearing action so practiced as toprevent air entrainment whereby to make the material fluid and mobileand then to return the same to the pot in a dispersed manner.

By so doing, I not only insured that there was a constant supply in thesystem of fluid glue for use in the spreaders, but also that I was ablethrough recirculation during the non-withdrawal periods of spreaderapplication to maintain fluidity in the container. Further, themechanical shearing action tended to reduce lumps of improperly mixedglue materials to a proper state of blending and smoothness through whatwas. in effect, a wet grinding operation. To a certain extent there wasalso to be observed a defoaming or foam depressing efiect upon the gluemix that of course was highly desirable. It should also be understoodthat my process produced a longer wet glue life, imparted more uniformspreading properties to the glue, and tended to reduce wood staining ofthe glue on the veneer as compared with chemcally reduced gluesincluding substantial amounts of caustic added for that purpose.

In the accompanying drawing I have shown a typical installation ofmechanism which can be employed to practice my process. A usual plywoodmill will have a floor It] above the floor on which most of themechanical steps followed in making plywood are practiced. The floor I0is usually that of a loft or gallery in which the glue mixing operationis conducted in a pot or container l2 having upper upright walls and alower converging hopper bottom M. The outlet of the hopper bottom I 4 ispractically directly into the casing of the shearing mechanism l6 whichI prefer to take the shape of a gear pump of conventional construction.The discharge outlet of the mechanism I6 is connected to the dischargeconduit I8 that is lead to a more or less remote spreading operationthat is conducted in a machine having the applicator roll 29, its doctorroll 22 and the backing roll 24. Usually such a spreader includestable-like plates 26, 28, over which the veneer 30 moves as it passesbetween rolls 29 and 24 to have glue applied to its upper surface. Theconduit l8 delivers glue to between rolls 2!] and 22 as shown in thedrawings by depositing it in the glue box 32. A valve 3| controls thedelivery of glue to ,the glue box.

For the purposes of creating a recirculation system for the gluematerial that is flowing out of the positive displacement pump I6 duringnonapplicating intervals of the spreader, I provide the return conduit36 that rises alongside the pot I2 to over its rim and thence down intothe pot to a suitably low level therein. Material flowing out of thedischarge end of conduit 36 is deposited upon the conical distributor orbaflle 38 where it tends to film out and flow throughout the contents ofthe pot in a, widely dispersed and distributed manner and with lowvelocity for the reasons earlier stated.

It is preferable that the lower conical portion 14 of the pot l2 besymmetrically shaped and of such a slope that the mere weight of theglue, especially in a gelled state, tends to crowd down toward theoutlet. If the slope is too flat or the container not properlysymmetrical, manual assistance as by the use of a paddle, will be neededto get the glue to the outlet and the shearing device [6.

The recirculation conduit 36 has a valve 49 therein close to the pointof connection of conduits 36 and 13. A preferable arrangement is toemploy a pressure relief valve at 40 which is normally closed when valve34 is open and opens when valve 34 is closed. Alternatively, valves 34and 40 have been pneumatically operated on oclems of long standing.Within the extensive experiences of people in the industry, thereappears never to have been an approach by way Of mechanical agitation ofthe gelled material. I believe this is true because it has notpreviously been understood that the material was thixotropic. This Ibelieve to be the essence of my discovery.

While I have spoken of the mechanical shearing device employed in theapparatus and designated 1-6 in the drawings as a gear pump, it shouldbe apparent that this element is essentialiv a positive displacementrotary pump and finds its equivalent in other than gear pumps so long asthere is a submerged shearing agitation or action practiced. It will beunderstood that other modifications and changes may be made in thecombination and arrangement of apparatus for practicing my processwithout departing from the scope and spirit of my invention.

What is claimed is:

1. A mechanism for processing and moving thixotropic materials,comprising: a container to receive a batch of thixotropic material, saidcontainer having a lower outlet opening; a pump connected in an airtight manner to said container at said outlet opening and located inclose proximity to said outlet opening; a return conduit connected in anair tight manner to said pump and leading to said container below thetop of said container and below the normal batch level in saidcontainer; and a baflle positioned in said container in close proximityto the discharge end of said return conduit in said container and inposition so that material flowing from said return conduit will impingeon said baflle and tend to be dispersed throughout said container, theimpingement surfaces of said baille being at a substantial angle to thedirection of the return flow.

2. The subject matter of claim 1 in which there is a discharge conduitconnected in an air tight manner to said pump for conveying saidmaterial from said container in which there is valve means for saidconduits to control flow from said pump through said pump; and whichsaid pump is a low velocity, high shearing positive displacement rotarypump.

3. The subject matter of claim 2 in which said container has an invertedconical shape; and said baffle has an upright conical shape and ispositioned between the discharge end of the recasion with the opening ofone synchronized to the closing of the other, nd vice versa.

My approach to the problem of undue thickening and gelling ofproteinaceous adhesive mixes has, in several installations, solvedprobturn conduit and the outlet opening; and in which said dischargeopening is axially located in the lower end of said container.

HENRY M. PREUSSER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PA'I'ENTB

